Flexible joints between the top portion of the riser and the floating structure need to handle up to about 20-25 degrees of angular displacement. The traditional way of terminating flexible risers underneath a floating unit is:
a) by extending them all the way to the deck or turret of the floating structure and using bending stiffeners to reinforce the knuckle point at the lower extremity of a guide tube, which is a tubular rigid structure firmly fixed to the deck or turret, or
b) by using a flexible joint at the lower extremity of a guide tube. Here the pipe extending up through a guide pipe as described in the referred patent may be strong enough for flexible pipes at moderate draughts, but as the risers are applied at greater water depths, and higher pressures, the riser tension is getting higher. As the tension is getting higher a transition in the industry towards using steel pipes instead of flexible pipes is taking place. The flexible part or ball joint connecting the catenary part of the riser with a short and stiff extension pipe/connection pipe inside the guide pipe will then be subjected to very high (moment) loads. The intention of the invention is to make a simple and maintainable interface between the top end of a riser and a floating structure, wherein a flexible part/ball joint at the top end of a riser is connected to an extension pipe/connection pipe (4 in FIG. 1) which in turn is connected to piping on a turret or other piping on a floating structure and may handle the high loads arising from greater depths and also centralize the pipe inside the guide pipe.